1. Field of the Invention
The invention relates to a method and apparatus for growing semiconductor crystalline materials in which a melt of the growing crystal is subjected to a magnetic field.
2. Discussion of Prior Art
Electronic devices are fabricated on wafers of semiconductor crystals. The properties of the semiconductor are heavily dependent on the specific impurities present in the wafers. Not all impurities are deleterious, and successful fabrication of electronic devices requires the control of the distribution and concentration of the impurities. For most electronic devices the starting material comprises a slice of wafer cut from a single crystal of the semiconductor, commonly either silicon or gallium arsenide. The crystal is in turn pulled from a melt. An object of this invention is an improvement to the techniques for the growth of semiconductor crystals which leads to improved homogeneity of certain impurities in the crystal.
Semiconductor crystals are for the most part grown from melts of the semiconductor in a crystal pulling apparatus. To control the electrical properties of the crystals, small quantities of specific impurities or dopants are added to the melt. One of the major problems in the production of crystals is to achieve control over the uniformity and concentration of dopants within the crystal.
During the growth process differences in composition or temperature between differing regions of the melt lead to density variations in the melt which can in turn have undesirable effects on the incorporation of impurities within the growing crystal and lead to the formation of localised fluctuations of impurity concentrations known as striae.